Numerical Investigations on the Impact of Base Angle of an Acute-Angled Trapezoidal Solar Air Heater Duct on the Flow and Thermal Characteristics Under Laminar Flow Environment

Abstract

Abstract. This article delineates the computational findings of thermal characteristics and fluid dynamics in acute-angled isosceles trapezoidal solar air heater (SAH) ducts functioning under laminar flow conditions. The duct base angle (θ) is altered from 45 to 90 deg, resulting in one triangular, four acute-angled trapezoidal, and one rectangular duct. The size of the solar radiation absorber plate is fixed at 0.16 m × 1.00 m across all the duct models. The SAH is exposed to a consistent and uniform heat flux of 1000 W/m2 with air flow Reynolds numbers (Re) ranging from 500 to 2000. Three-dimensional computational simulations were functioned using ansys fluent software. A few computational outcomes are cross-checked with the literature data and selective experiments. A comprehensive assessment of the Nusselt number, rise in air temperature, and friction factor via the ducts is accomplished. The prime goal of SAH is to acquire an elevated air temperature at the duct exit. So, it is established that the triangular SAH duct performance is approximately 46.51% higher than that of the rectangular duct, at Re = 500. Moreover, a comparative assessment of the previously published data of Dara and Muvvala [2023, “Effect of Base Angle of an Isosceles Trapezoidal Solar Air Heater Duct on Flow and Thermal Characteristics—A Numerical Investigation,” ASME J. Sol. Energy Eng., 145(4), p. 041008] under turbulent flow conditions is made with the present outcomes under laminar flow, and it is witnessed that the SAH performance is superior under laminar flow conditions. Following the acquisition of optimal geometry of the duct, further analysis is conducted by varying the heat flux conditions and incorporating dimple protrusions on the absorber plate. It is found that for rectangular SAH ducts, by including dimples on the absorber plate, the Nuavg and favg values are increased by roughly 20.45% and 7.97%, respectively, in contrast to the duct without dimples.